REQUIREMENTS AND INDUSTRIAL APPLICATIONS OF CLAYS IN MANUFACTURING OF FAST FIRED SINTERED UNGLAZED TILES

T.Manfredini¹ and M.HanuskovÁ²

¹ Department of Chemistry, Faculty of Engineering, University of Modena, Via G. Campi 183, 41100 Modena, Italy, e-mail: manfredini@pascal.unimo.it

² DEMOCenter s.r.l., Viale Virgilio 55, 41100 Modena, Italy; e-mail: lab.car-mat@democenter.it

Abstract

Clay based minerals are the main components of unglazed porcelainized stoneware ("grčs porcellanato") bodies and their amount generally ranges from 40 to 60 wt%. They confer plasticity and workability in the green state and fournish the main oxides involved, with fluxes and other sintering aids, in the strengthening mechanism of the body during firing. The clays used should have properties advantageous for modern continous wet-processing (i.e. dispersion in water), workability (plasticity, viscosity, body formation, drying behaviour, dry bending strength, sintering and firing behaviour) and low contents of impurities (colour and transparency of the body). Kaolinitic clays can improve the formation of mullite and, in general, by widening the sintering temperature range reduce swelling and deformation of tiles during firing. Low titanium and iron oxides content is foundamental in developing colours.